Optical properties of tetrahedral amorphous carbon nitride

we calculated the optical properties of three amorphous tetrahedral carbon- based clusters of the type a - C21-iNiH28 with 6-atom boat-type rings. The 28 hydrogens passivate the outermost dangling bonds and i is 0, 1 or 4. The theoretical DFT-LDA based method used minimizes the energy of the clusters and provides the energy spectrum and the optical transitions for the minim um energy structures. The optical absorption spectrum is analyzed for each cluster and is consistent with previous results obtained by the authors for the behaviour of the energy gap.